In this specification, the term “air-conditioners” generally and collectively means air heating, cooling, drying, moistening and other air conditioning devices, apparatuses, systems and installations for succinctness unless the context requires otherwise. Likewise, the term “ventilators” generally and collectively means ventilating or air-circulating means, devices, systems or installations for succinctness, unless the context otherwise requires. Throughout this specification, the term ventilators, ventilating apparatus and air-conditioners may be considered equivalent to the extent appropriate.
Air-conditioners are widely used to provide comfortable indoor conditions for occupants of residential, commercial or public buildings, premises or other enclosed spaces such as offices, schools, cinemas, theatres, halls, and other similar places. However, while many air-conditioners are provided with means to remove stale indoor and introduce fresh out-door air, their performance is not entirely satisfactory. In fact, there have been reports that the indoor carbon-dioxide concentration in many air-conditioned schools exceeds the generally acceptable level of 800 ppm by as much as 35%.
To supplement the performance of air-conditioners, ventilators may be used with or built-in to air-conditioners so that indoor air, which may contain a high concentration harmful gases, can be constantly and regularly replaced with air supply which has a higher oxygen content and a lower harmful gas content. Typical harmful gases found in enclosed buildings, especially crowded buildings, include carbon-dioxide, carbon-monoxide, unpleasant odors, irritants and harmful gases such as formaldehyde in the building materials and the radioactive radon gas released from granite.
On the other hand, although out-door air generally has a higher oxygen content, it is not without pollutants and air-pollution is especially bad in heavily built-up urban or city areas. Typical pollutants found in out-door air include particulate pollutants such as dusts, ashes, smoke particles, particles from incomplete combustion of diesel fuel, pollens, odors, acid or other chemical gases, and bacterial organisms.
In order to block, or at least minimise, the entrance of harmful substances into an enclosed indoor space to provide a healthier indoor environment, ventilators or air-conditioners are usually provided with air filters at the “fresh-air” intake ports. The air filters may be simple mesh filters or more sophisticated filters such as activated carbon filters, polymeric foam filters, glass fiber filters and biostat filters such as those containing potassium permanganate are useful alternatives or additions. In some applications, high-efficiency particulate air (HEPA) filters which are known to be effective to remove up to 99.7% of air-borne particles of the size of 0.3 microns or larger, can be used. Some air filters for use in air-ventilators may include one or more types of filtering materials and designs in order to optimally removed different types of harmful substances from the supply air.
Since the conditioned indoor air to be exhausted usually or, as a norm, contains re-usable thermal energy, it is desirable that such ventilators are provided with thermal exchangers so that reusable thermal energy can be exchanged between the in-coming and the out-going air streams. With this energy recycling process, an additional supply of out-door air into an enclosed indoor space can be provided with less energy costs or wasted energy.
Examples of ventilators with thermal exchangers are described in the following U.S. Patents: U.S. pat. No. 5,238,052, U.S. pat. No. 4,874,042, U.S. pat. No. 4,377,400. In those examples, thermal exchangers are utilized to recover thermal energy from the out-going air stream to reduce wasted thermal energy discharged from the exhaust air. This recouperation of energy is beneficial for the protection of the environment, as well as imposing a lesser load or demand on the air-conditioners and, at the same time, reducing the operating and running costs of air-conditioners. Such benefits are achievable because it is known that thermal exchange between a cold air stream and a hot air stream will reduce the total energy requirement for conditioning the in-coming air stream. Thus, for an air-cooling system, the in-coming air stream is cooled by the out-going or exhaust chilled air before the exhaust air leaves the air-conditioner. Similarly, for an air-heating system, the out-going warm air is used to warm up the in-coming out-door air before it enters a building.
It is therefore desirable to provide ventilators with high efficiency air filters which operate with high thermal efficiency and low running costs so that the environment can be protected, wasted heat as well as energy costs can be reduced. As space is usually precious in city areas, it is also desirable that the improved ventilators are simple and compact. Preferably, important parts or components, such as the thermal exchanger unit, of the air-ventilators are of modular design for easy maintenance. In addition, while the air-ventilator can be used as a stand-alone unit, it is desirable that the improved air-ventilators can be incorporated or used in or with air-conditioners.
In light of the afore-mentioned requirements for contemporary air-conditioners, it is highly beneficial and desirable that air-conditioners incorporating thermal exchangers as well as highly efficient air filters with high durability and reliability are provided. However, it has been observed that the performance of conventional air-conditioners of this description degrades after an extended period of use. Hence, it is highly desirable that air-conditioners or ventilators with highly efficient thermal exchangers and air filters which can provide a stable performance over a period of extend use can be provided. At least, such ventilators should have a design which can be easily or conveniently maintained for consistent performance.